I. Field of the Invention
The present invention relates to apparatus for manipulating heavy objects and more particularly to such an apparatus including means for rotating an object around its longitudinal axis while the object is suspended to facilitate work being performed on the object.
II. Description of the Prior Art
An apparatus for rotating a heavy object about its longitudinal axis while the object is suspended such apparatus including a horizontal beam adapted to be lifted by a crane and a pair of driving units slidably attached to said beam for revolving endless cords supporting the heavy object has been known. Each of the driving units is provided with a reversible electric motor which drives pulleys.
In use, the position of the driving units is adjusted by sliding them along the horizontal beam in dependence upon the length and weight of the object to be rotated so as to distribute the weight of the object equally to the driving units. After the end portions of the objects are inserted into the lower loop portions of both endless cords respectively, the horizontal beam together with the driving units are lifted by means of a crane. When both endless cords tighten enough to suspend the object, the electric motors of both driving units are started simultaneously so as to revolve the endless cords in the same direction so as to rotate the object to the desired position.
Such apparatus is useful to carry out welding operations on heavy objects such as trusses, honey combs and the like, but it has the disadvantage of the horizontal beam being subjected to great bending moments due to the heavy object as well as the risk of slip of the cords on the pulleys and disengagement of the cords from the pulleys when the cords slacken.